Development of a portable type open-window-ionization chamberin mammography

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In order to perform accuracy management based on the measurement value of the correct dose in mammography, in dose measurement of the low energy X-rays from mammography equipment , the portable type open-window-ionizationchamber which the characteristic of response does not vary was developed. In order to consider it as a portable type unlike the conventional free -ionization chamber, the shape of a collector electrode and arrangement were considered. The energy dependence and the evaluation of absolutely measurement of experimental model of an ionization-chamber were performed using the dose standard place with the same energy spectrum as the equipment used in mammography screening of X-rays. The linearity of dose rate dependence was good to ～15 mGys-1. In the energy range of the X-rays from tube voltage 23 kV to 110 kV, change of the response of a detector was less than 3 %. Moreover, dark current is 10-14～-15A, and it checked that the stable measurement value was obtained for a long time. The portable type open-window-ionization-chamber developed by a new concept can implement highly accurate and stabilized measurement in case of dose evaluation required for the accuracy management in the mammography equipment currently installed in medical facilities.